> ## Documentation Index
> Fetch the complete documentation index at: https://prefab.prefect.io/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Local Preview

> Preview PrefabApp UIs in your browser without an MCP host.

`prefab serve` renders a `PrefabApp` as a self-contained HTML page and serves it locally. This lets you iterate on layouts, styling, and client-side interactions (state, forms, conditionals) without wiring up an MCP server or host application.

## Quick Start

Create a Python file that defines a `PrefabApp`:

```python app.py theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
from prefab_ui.app import PrefabApp
from prefab_ui.components import Heading, Text

with PrefabApp(state={"greeting": "Hello"}, css_class="p-6") as app:
    Heading("Hello Prefab")
    Text("This is a local preview.")
```

Then serve it:

```bash theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
prefab serve app.py
```

This opens your browser to `http://127.0.0.1:5175` with the rendered UI. All client-side behavior works — state binding, `SetState`/`ToggleState` actions, `ForEach` loops, conditional rendering, form submissions. The only thing that won't work is `CallTool`, since there's no MCP server to call back to.

## Auto-Discovery

If your file has a single `PrefabApp` instance, `prefab serve` finds it automatically. If there are multiple, point to the one you want:

```bash theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
prefab serve app.py:dashboard
```

## Live Reload

Pass `--reload` to watch for file changes and regenerate the page on save:

```bash theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
prefab serve app.py --reload
```

This watches all `.py` files in the same directory as your target file. When a change is detected, it re-executes the module and regenerates the HTML. Refresh your browser to see the update.

## Options

| Flag                       | Default       | Description               |
| -------------------------- | ------------- | ------------------------- |
| `--port`, `-p`             | `5175`        | Port for the local server |
| `--reload` / `--no-reload` | `--no-reload` | Watch for file changes    |

If the requested port is in use, `prefab serve` automatically finds the next available one.

See [PrefabApp](/reference/app) for the full API reference.